In recent years, as environmental issues, energy issues and other similar issues are addressed, hybrid vehicles, electric vehicles, fuel cell vehicles and other similar motored vehicles are gaining attention. These motored vehicles have a direct current power supply implemented by a secondary battery or a fuel cell, an inverter and a motor driven by the inverter as a power source.
Japanese Patent Laying-Open No. 2004-203218 discloses a control device that is provided in a motored vehicle provided with a transmission between a motor generating driving force and an output member and corrects a torque output of the motor when the transmission is shifting gears. When the transmission is shifting gears, the control device corrects the torque of the motor in a direction that suppresses variation of the torque of the output member to prevent the torque of an output shaft from dropping as the transmission shifts gears.
Furthermore, as motors increasingly provide larger outputs, the above described motored vehicle is also known that is provided with an upconverter receiving direct current voltage from a direct current power supply to upconvert the received voltage to supply the upconverted voltage to an inverter.
Japanese Patent Laying-Open No. 2004-208409 discloses a vehicular power control device including such an upconverter. The vehicular power control device includes a driving, rotating electric machine, an inverter circuit driving the driving, rotating electric machine, and a DC-DC converter receiving voltage from a battery to upconvert the received voltage to supply the inverter circuit with the upconverted voltage. This vehicular power control device can reduce an up-conversion ratio of the DC-DC converter in accordance with the electric power consumption of the driving, rotating electric machine in driving the driving, rotating electric machine with small electric power. The vehicular power control device can thus reduce a loss in a circuit.
If a motored vehicle provided with a transmission between a motor generating driving force and a driving wheel is provided between a direct current power supply and an inverter with an upconverter outputting a voltage, which corresponds to that input to the inverter, controlled in accordance with the output of the motor, and as the transmission shifts gears, the output of the motor abruptly varies and accordingly the voltage output from the upconverter, i.e., that input to the inverter, is modified, then, for some motor control modes, there is a possibility that the motor is unstably controlled.
When the transmission is shifting gears, the transmission has a friction element re-engaged and accordingly the motor rotates at an increased rate. If this is prevented by exerting control to temporarily decrease a torque output of the motor when the transmission is shifting gears, (hereinafter also referred to as “torque reduction control”), then when the transmission is shifting gears, the motor provides an output decreasing and increasing (or recovering) for the former and latter halves, respectively, of shifting gears, and modifying the voltage output from the upconverter, i.e., that input to the inverter as the output of the motor abruptly varies when the transmission is shifting gears, allows the inverter to receive a voltage decreasing for the former half of shifting gears as the output of the motor decreases and increasing for the latter half of shifting gears as the output of the motor increases. Note that if the motor is controlled in a rectangular-wave control mode, which has a larger interval in timing to control the motor than a PWM control mode and is based on that the inverter receives constant voltage, the switching operation in the inverter cannot follow the abrupt variation in the voltage input and the motor is unstably controlled.